Methyltransferases (EC 2.1.1.-) constitute an important class of enzymes present in every life form. They transfer a methyl group most frequently from S-adenosyl L-methionine (SAM or AdoMet) to a nucleophilic acceptor such as oxygen leading to S-adenosyl-L-homocysteine (AdoHcy) and a methylated molecule [PMID: 16225687, PMID: 21858014, PMID: 12826405]. All these enzymes have in common a conserved region of about 130 amino acid residues that allow them to bind SAM [PMID: 7897657]. The substrates that are methylated by these enzymes cover virtually every kind of biomolecules ranging from small molecules, to lipids, proteins and nucleic acids [PMID: 16225687, PMID: 21858014, PMID: 7897657]. Methyltransferase are therefore involved in many essential cellular processes including biosynthesis, signal transduction, protein repair, chromatin regulation and gene silencing [PMID: 16225687, PMID: 21858014, PMID: 12826405]. More than 230 families of methyltransferases have been described so far, of which more than 220 use SAM as the methyl donor.